Adam Bieńkowski

Magnetoelastic Villari effect in Mn–Zn ferrites

Abstract The relationship between magnetic induction B, and compressive stress −σ in Mn–Zn ferrites, of very low magnetostrictive constant λs, were investigated. The Villari effect and its technical importance is discussed. It is shown that in Mn–Zn ferrites, with λs≈0, the Villari point occurs for σ≈0 and that these ferrites exhibit, for σ ≫0 , considerable magnetoelastic sensitivity — in spite of their small λ s value. Hence, a low magnetostriction constant λs does not exclude the possibility to apply such materials in magnetoelastic sensors.

The magneto-elastic Villari effect in ferrites

Abstract The relationship between magnetic flux density B , and stress σ in ferrites is presented. The origin of the Villari effect and its technical importance is discussed. It is shown that the position of the Villari point and piezomagnetic sensitivity depend on the same properties of a material as those governing the B ( H ) relation.

Low Current Transformer Utilizing Co-Based Amorphous Alloys

Metal oxide surge arresters have been widely used for protection of power system networks against overvoltages caused by atmospheric discharges or malfunction of devices connected to the network. During its operation, a surge arrester structure is degradated, which can be observed as an increase of a surge arrester leakage current. This paper presents an implementation of a new, high-permeability, Co64Fe4Ni1Si15B14 amorphous alloy as a current transformer for monitoring of a leakage current in low voltage surge arresters. The characteristics of the current transformer for different loads have been measured in the system using very sensitive current-voltage converter. Experimental results confirmed that low current transformer utilizing Co64Fe4Ni1Si15B14 amorphous alloy in annealed state gives a possibility to measure a leakage current about several μA with operating frequency 50 Hz. Moreover, the results indicate that the leakage current waveforms have a different shape than a pure sine wave voltage applied to the surge arrester enabling an evaluation of the device nonlinearity as a measure of its degradation by means of a resistive component of the leakage current.

Effects of stress and its dependence on microstructure in Mn–Zn ferrite for power applications

Abstract The relationship between magnetoelastic properties and microstructure has been studied for a series with different bulk density of Mn 0.70 Zn 0.24 Fe 2.06 O 4 ferrite for switch mode power supplies applications. It is shown that in investigated ferrites, in spite of their small λ s value (equal 0.6×10 −6 ), the effect of stress is considerable. The course of magnetoelastic characteristics B ( σ ) H and H c ( σ ) H of investigated Mn–Zn ferrites depends significantly on its microstructure.

Some problems of measurement of magnetostriction in ferrites under stresses

Abstract Problems of measurement which cause difficulty in investigating the magnetostrictive properties of ferrites under stresses are concerned with: (i) considerable brittleness of ferrites, (ii) non-uniform distributions of applied stresses on investigated sample, (iii) small values of λ s of ferrites. In this paper the above problems are discussed.

Magnetostriction of Ni-Zn ferrites containing cobalt

Abstract The influence of a small cobalt content on the magnetostriction of Ni-Zn ferrites has been investigated and is discussed. It is shown that, as in the case of a magnetocrystalline anisotropy, the value of λ s may in this case be quite different from that expected. The results prove that, in spite of common opinion, there are no “piezomagnetic obstacles” to introducing Co ions into Ni-Zn ferrites, when the diminishing of their magnetic loss factor in high frequency range is needed.

The dependence of Villari effect in ferrites on their magnetocrystalline properties and magnetostriction

Abstract The dependence of localization of the Villari point and piezomagnetic sensitivity on the magnetostriction and other material properties are discussed. The discussion is based on B(σ)H and λ(H) relations for ferrites of different chemical compositions. By measurements of B(σ)H in the range of both positive and negative values of σ it was confirmed the expectation that the Villari point for the ferrite with λ=0 occurs for σ≈0. Variation of the ZnO content in Ni-Zn ferrite can be used to control the piezomagnetic sensitivity in a limited range only. The B(σ)H relations seem to be the most explicit data with regard to estimation of the piezomagnetic properties of ferrites.

Effect of stresses on the magnetostriction of Ni-Zn(Co) ferrites

Abstract The effect of stress-dependent magnetostriction λ∣ and λ⦜ in Ni-Zn ferrites containing cobalt is investigated. Under applied compressive stress the magnetostriction changes its sign at some -σ value which corresponds to the -σ value of the Villari point.

Application of Extended Jiles–Atherton Model for Modeling the Magnetic Characteristics of Fe

This paper presents the result of modeling the magnetic characteristics of ring-shaped cores made of Fe41.5Co41.5Nb3Cu1B13 alloy in both as-quenched and nanocrystalline state. For the modeling, the extended Jiles-Atherton model was used. Extension of Jiles-Atherton model is focused on taking into account the changes of parameter k caused by changes of the average energy required to break pinning site. Determination of models parameters was made on the base of optimization process. This optimization covered both evolutionary strategies and simulated annealing. Finally, good agreement between experimental characteristics and the results of modeling was achieved. This agreement is confirmed by the high value of R2 determination coefficient, which exceeds 99% for both as-quenched and annealed cores. As a result, it was confirmed that the presented method of modeling the magnetic characteristics of Fe41.5Co41.5Nb3Cu1B13 alloy in both as-quenched and nanocrystalline state is suitable for technical applications.

_{41.5}

Paper presents the frame-shaped cores based methodology of testing of magnetoelastic characteristics of energetic steels such as X30Cr13 steel, subjected to tensile stresses. In presented method, the magnetic circuit of the sample is closed. For this reason, the results of magnetoelastic investigation are independent of the shape of the sample. To validate the proposed method, the influence of tensile stresses on B(H) hysteresis loop of X30Cr13 martensitic corrosion resistant steel was carried out. On the base of these result, clear criteria for non-destructive assessment of mechanical stresses in the material were determined.